A light-emitting diode (LED) is a semiconductor diode that emits incoherent narrow-spectrum light when electrically biased in the forward direction of the p-n junction. LEDs produce more light per watt than incandescent bulbs. LEDs are often used in battery powered or energy-saving devices and are becoming increasingly popular in higher power applications such as flashlights, area lighting, and regular household light sources.
LED performance largely depends on the ambient temperature of its operating environment. Driving the LED hard in high ambient temperatures may result in overheating of the LED package, resulting in poor performance and eventually leading to device failure. Consequently, adequate heat-sinking or cooling is required to maintain a long lifetime for the LED, which is especially important in automotive, medical, and military applications where the LED must operate over a wide range of temperatures and is required to have a low failure rate.
Generally, LED cooling systems rely largely on convective mechanisms to remove heat. Heat convection refers to heat transport by an external source, such as a fan, or heat transfer caused by buoyancy forces resulting from density differences caused by temperature variations in a fluid. The use of passive thermally conductive materials that absorb the heat and slowly rise in temperature would be highly impractical for longer term thermal dissipation. For a non-limiting example, the size of a piece of aluminum needed to cool LEDs used in a typical lighting application for a time span of eight hours or more would be so large that the aluminum would never come to saturation and the LEDs would unacceptably spike up in temperature. The reason is that the volume of the aluminum required to store the heat generated by the LED is beyond the size constraints of the LED bulb envelope, the amount of aluminum required for this application is impractically massive, and aluminum inefficiently facilitates heat convection because it experiences a linear temperature rise proportional to stored heat so that the thermal capacity required for a given LED power level and operating time is very large.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent upon a reading of the specification and a study of the drawings.